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The Cell Membrane in the Steady State
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
An ion channel consists of a receptor-type protein, referred to as a channel protein, or aquaporin, which surrounds an aqueous pore that forms a direct connection between the external and internal aqueous media. The pore allows passage of ions between these two media, subject to certain restrictions. The channel protein may have some carbohydrate groups attached to it on the extracellular side (Figure 2.2). Since ion channels and their aqueous pores are central to the electrical properties and behavior of the cell membrane, they will be considered here in a little more detail.
Cholangiocyte Ion Channels:
Published in Gianfranco Alpini, Domenico Alvaro, Marco Marzioni, Gene LeSage, Nicholas LaRusso, The Pathophysiology of Biliary Epithelia, 2020
In contrast, ion channel proteins contain an aqueous pore that opens to allow rapid movement of ions across the membrane at rates of above 10 10 ions sec−1, values several orders of magnitude greater than ATPases and cotransporters. The molecular diversity responsible for the many different channel types is impressive, but they can be characterized by their common features. First, channels exhibit selective permeability to specific ion types. In the example shown, the pore is selectively permeable to Cl− ions because the cationic charges that line the pore domain function as a permeability filter excluding charged cations. Thus, according to the underlying structure, channels are characterized as Cl− channels, Na+ channels or K+ channels based on the observed pore properties. In some cases the selectivity can be extreme. For example, certain K+ channels exhibit selective permeability K+ over Na+ ions of 100:1 despite a similar molecular radius and charge. In contrast, other channel types discriminate rather poorly. This relative lack of selectivity appears to be true for many CI” channels, since channel opening allows movement of HCO3− and other organic anions across the plasma membrane.
Chemical– and Drug–Receptor Interactions
Published in Frank A. Barile, Barile’s Clinical Toxicology, 2019
Ion channels represent a diverse group of integral membrane proteins that regulate the passage of ions across cell membranes. They are ubiquitously expressed throughout the body and are essential for important physiological processes such as regulation of membrane potential, signal transduction, and cellular plasticity. Defective ion channel proteins are associated with cystic fibrosis, the long-QT syndrome, heritable hypertension (Liddle’s syndrome), hereditary nephrolithiasis (Dent’s disease), and a variety of hereditary myopathies, including generalized myotonia (Becker’s disease) and myotonia congenita (Thomsen’s disease). Table 11.1 illustrates drugs that target ion channels.
Ionotropic glutamate receptors in platelets: opposing effects and a unifying hypothesis
Published in Platelets, 2021
Maggie L. Kalev-Zylinska, Marie-Christine Morel-Kopp, Christopher M. Ward, James I. Hearn, Justin R. Hamilton, Anna Y. Bogdanova
Within their own types, subunits initially assemble in the endoplasmic reticulum as dimers (homomeric or heteromeric) and then organize into tetramers (dimers of dimers) to form mature receptors in the plasma membrane. The extracellular portion of the receptor contains the amino-terminal (ATD) and agonist-binding domains (ABD) that bind receptor modulators and ligands, respectively. The M1-M4 transmembrane segments form a pore of the ion channel (Figure 1B and C). The tip of the M2 loop contains the Q/R/N site subject to frequent editing at the mRNA level (Figure 1A and C; red marks) [10]. Editing controls Ca2+ permeability in AMPAR and KAR, and both Ca2+ permeability and Mg2+ block in NMDAR [11]. The intracellular C-terminal domain provides interaction with other proteins to help propagate the receptor signal downstream (Figure 1B) [2].
The relevant targets of anti-oxidative stress: a review
Published in Journal of Drug Targeting, 2021
The protective effect of ischaemic preconditioning on myocardium has been confirmed by a large number of experiments. Recent studies have shown that short-term myocardial ischemia-reperfusion can induce the up-regulation of many protective genes, such as antioxidant enzyme genes and NO synthase. Regulating the functional and metabolic changes of myocardium after ischemia-reperfusion is an important part of the myocardial endogenous protective mechanism, and it is also one of the important molecular bases for the myocardial protection of ischaemic preconditioning. Based on rat myocardial ischemia-reperfusion animal model, Jiang et al. screened the possible interaction proteins of MIP2 and identified voltage-dependent anion channel (VDAC), including VDAC1, VDAC2 and VDAC3 [120]. They found that VDAC1 might be a potential target for MIP2, and WD40 at the C-terminal of MIP2 is a domain that interacts with VDAC1. MIP2 can inhibit the reduction of mitochondrial membrane potential and cell death of cardiomyocytes induced by oxidative stress, and its mechanism may be related to the regulation of VDAC1.
Non-thermal membrane effects of electromagnetic fields and therapeutic applications in oncology
Published in International Journal of Hyperthermia, 2021
Peter Wust, Ulrike Stein, Pirus Ghadjar
We validated the non-thermal effects of RF at 13.56 MHz without AM in a typical preclinical experiment using LabEHY-200 [55]. For a better understanding, we developed a model for ion channels based on textbook knowledge [112–115]. Figure 4 shows an example of a Ca2+ channel, which was proven to be particularly important for non-thermal effects. This model is also extrapolatable to potassium (K+), sodium (Na+), chloride (Cl–) or hydrogen (H+) ions. The basic elements of a typical ion channel are the entrance (here outer) pore, which has a mechanism for opening and closing (gating) with some selectivity for the particular ion (here Ca2+), a cavity to collect the ions, and the selectivity filter as the most important and highly specific part for the particular ion. The ion gains the dehydration energy by a specific chemical reaction with carbonyl oxygen atoms lining the selectivity filter, stalls in the filter, and can only exit by exploiting electrostatic repulsive forces if the next ion enters from the cavity [112].